Lamp bulbs of the type commonly known as wedge base bulbs are in wide use in many environments including in automobiles wherein they are used for panel lighting and for other purposes. Wedge base bulbs have a glass envelope containing the filament with the base of the envelope itself being designed to be wedged into a receiving socket. Of particular significance is the fact that such bulbs do not have a metallic base like many other forms of lamps. Instead, the connections to the internal filament are made through conductors which extend through the base end of the envelope and are bent backwards over the exterior surface of the wedge base thereof. Electrical energy is then supplied to the bulb by bringing contact elements into engagement with those conductors in various ways.
Wedge base bulbs and bulbs of similar types and sockets for use therewith are shown in a number of issued U.S. Pat. Nos. including 3,143,301; 3,208,032; 3,253,249; 3,339,172; and 3,617,984.
The wedge base bulb has many advantages over screw and bayonet base bulbs, including lower costs for the bulb and the socket to receive it, and increased reliability, both as to the bulb itself and also as to the use of the bulb. For example, the probability of a screw base bulb working itself loose as a result of vibration in an automobile is somewhat greater than with either a bayonet base type or a wedge base type, and bayonet bases tend to corrode in their sockets, rendering replacement more difficult.
Thus, there is considerable increased interest in wedge base bulbs and attention has turned to developing inexpensive and reliable sockets for them. One such approach which has been used is to fabricate leaf type contact elements to engage the conductors of the bulb and to then mold a non-rigid material around the contacts to form the socket into which the bulb can be inserted. The outside configuration of the socket is typically designed to snap into a mounting hole. Experience has shown that there are several difficulties with this approach. For one, the mounting holes formed in an automobile body commonly have sharp edges which can easily slice through the relatively soft non-rigid material, seriously damaging the socket. However, it is not possible to simply make the material harder and more rigid because the socket must be sufficiently resilient to permit insertion of the bulb without excessive force and to press the molded-in contact members against the bulb conductors. Such sockets for use in automobiles must meet rather rigid SAE specifications as to insertion force, etc.
An additional problem with molded-in contacts is the difficulty of keeping the contact surfaces of the molded-in contacts free of the socket material which, of course, is an electrical insulator. Even a small amount of material on that surface renders the socket inoperative.
Still further, the sockets with molded-in contacts involve costly manufacturing processes involving the loading of the electrical contacts into the mold cavities, and there is substantial difficulty in maintaining dimensional characteristics due to the soft molding material.
In addition, it is not presently possible to make a flexible socket with thermoforming materials which can withstand temperatures exceeding about 125.degree. F. (52.degree. C.).
Attempts to overcome these problems have resulted in the use of contact members which snap into pre-molded sockets. However, these efforts have not been fully successful and have resulted in sockets with exposed terminals, light leaks through the rear ends of the sockets, high molding costs as a result of complex molds with slides, cams and the like, or terminals which fail to lock properly and securely into the pre-molded housings.